1. Field of the Invention
The present invention relates generally to blowout preventers used in the oil and gas industry. More particularly, the present invention relates to a removable seal carrier for a blowout preventer bonnet assembly.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well in, for example, oil and gas exploration applications, devices must be put in place to prevent injury to personnel and equipment associated with drilling activities. One such well control device is known as a blowout preventer (BOP).
Blowout preventers are generally used to seal a wellbore. For example, drilling wells in oil or gas exploration involves penetrating a variety of subsurface geologic structures, or “layers.” Generally, each layer is of a specific geologic composition such as, for example, shale, sandstone, limestone, etc. Each layer may contain trapped fluids or gas at different formation pressures, and the formation pressures increase with increasing depth. The pressure in the wellbore is generally adjusted to at least balance the formation pressure by, for example, increasing a density of drilling mud in the wellbore or increasing pump pressure at the surface of the well.
There are occasions during drilling operations when a wellbore may penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with this “kick” is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high pressure “kick” tends to propagate from a point of entry in the wellbore uphole (from a high pressure region to a low pressure region). If the “kick” is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. These blowouts often result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and in substantial injury or death to rig personnel.
Because of the risk of such blowouts, blowout preventers are typically installed at the surface or on the sea floor in deep water drilling water arrangements so that “kicks” may be adequately controlled and circulated out of the system. Blowout preventers may be activated to effectively seal in a wellbore until active measure can be taken to control a “kick.” There are several types of blowout preventers, the most common of which are annular blowout preventers and ram-type blowout preventers.
Annular blowout preventers typically use annular elastomer “packers” that may be activated by, for example, inflation, to encapsulate drillpipe and well tools and completely seal the wellbore. The second type of common blowout preventer is the ram-type blowout preventer. Ram-type blowout preventers typically are formed by a body and at least two bonnet assemblies disposed on the body and opposite of each other with respect to a circumference or perimeter of the body.
FIG. 1 shows an example of a ram-type blowout preventer 10. The blowout preventer 10 is formed by a body 12 and oppositely disposed bonnet assemblies 14. The blowout preventer 10 further includes a plurality of side openings 20 that are each adapted to be coupled to a bonnet assembly 14.
FIG. 1 shows a bonnet assembly 14 that may be secured to the body 12 using a radial lock mechanism to allow for maintenance access. A radial lock mechanism for blowout preventers is disclosed in U.S. Pat. No. 6,554,247, which is assigned to the assignee of the present invention and is incorporated herein by reference in its entirety. FIG. 1 also shows bonnet assemblies 14 that are coupled to the blowout preventer body 12 by a slidable coupling. A slidable coupling is disclosed in U.S. Pat. No. 6,510,897, which is assigned to the assignee of the present invention and is incorporated herein by reference in its entirety. Alternatively, in other typical blowout preventer designs, bonnet assemblies are generally secured to a body of the blowout preventer about the circumference of the body with, for example, bolts.
Inside of a bonnet assembly is a piston actuated ram. The rams may either be pipe rams, which, when activated, move to engage and surround drillpipe and well tools to seal the wellbore, or shear rams, which, when activated, move to engage and physically shear any drillpipe or well tools in the wellbore. The rams, whether pipe-type or shear-type, are typically located opposite of each other and typically seal against one another proximate a center of the wellbore in order to completely seal the wellbore.
As with any tool used in drilling oil and gas wells, blowout preventers must be regularly maintained. For example, a blowout preventer uses high pressure seals between bonnet assemblies and the body of the blowout preventer. FIG. 2 shows a prior art bonnet assembly 100. The bonnet assembly 100 includes a face 103 that is engaged with a corresponding face of a blowout preventer body (e.g., 12 in FIG. 1) when the bonnet assembly 100 is installed on the blowout preventer. The bonnet face 103 includes a face seal 105 that seals the high pressure inside the blowout preventer body (e.g., 12 in FIG. 1) and the bonnet assembly 100.
The high pressure seals in many instances are elastomer seals. The elastomer seals must be regularly checked to ensure that the elastomer has not been cut, permanently deformed, or deteriorated by, for example, chemical reaction with the drilling fluid in the wellbore. Moreover, it is often desirable to replace seals to ensure that the bonnet will be properly sealed in the event of a kick. Therefore, it is important that the blowout prevent bonnet include components that are easily removable so that seals may be easily accessed, checked, maintained, and replaced.